Hydrogen evolution reaction mechanism on 2H-MoS2 electrocatalyst

Abstract The edges of hexagonal symmetry molybdenum disulfide (2H-MoS2) are usually considered as active sites for hydrogen evolution reaction (HER). However, the underlying HER reaction mechanism, particularly its reaction kinetics on 2H-MoS2, have not been widely studied. In this work, a systemic density functional theory (DFT) study on HER pathways and reaction kinetics on basal and edges planes of 2H-MoS2 is presented, in which the solvent effect is explicitly considered. The results show that, regardless of the basal or edge plane, at the S sites of 2H-MoS2, HER is more likely to proceed through the Volmer-Heyrovsky pathway, and the activity of the edge S is higher than the basal S. In the latter, HER was hindered by the Volmer step, which requires an energy barrier of 0.65 eV to “attract” the H from hydronium ion water (H3O+) onto the basal S sites. On the edge Mo sites, both Volmer-Tafel and Volmer-Heyrovsky pathways are favorable, and their reaction kinetics can be promoted through the synergetic effect of its adjacent S and the adsorbed H2O. These results provide new fundamental insights on the HER mechanism on 2H-MoS2.